feat(updater): silent background pre-download and instant install for Compose updater - #1

Summary

Builds directly on top of your recloudstream#3204 Compose updater architecture by introducing silent background pre-downloading and immediate installation from cached APKs with real-time in-app progress.

What this adds to recloudstream#3204

1. Silent Background Pre-download:

   • In \ApkUpdater.kt, added \downloadSilently\ to fetch updates in the background without UI interruption during automated checks (\AutoSearchForUpdate).
   • The user is only notified once the APK is fully downloaded and verified on disk.

2. Instant Install from Cache:

   • In \GithubViewModel.kt, clicking Update checks if the APK is already pre-downloaded in internal cache.
   • If present, \ApkUpdater.installFromFile\ immediately writes to \PackageInstaller.Session\ without download wait times.
   • Falls back gracefully to standard live download if cache is missing.

3. In-App Installation Progress in Compose:

   • Added \GithubUpdateDialogState.InstallProgress\ to \MainActivityScreen.kt.
   • Displays real-time 0%–100% horizontal progress while writing to the session.
   • Re-enabled \AutoSearchForUpdate\ on \MainActivityScreen\ to allow automated background update discovery.

Verification

• Built full APK via ./gradlew assemblePrereleaseDebug\ (Build Successful).
• Verified Kotlin compilation and ABI compatibility.